The invention relates to transducers and more particularly to vibration transducers for loudspeakers comprising panel-form acoustic radiating elements.
It is known from GB-A-2262861 to suggest a panel-form loudspeaker comprising
a resonant multi-mode radiator element being a unitary sandwich panel formed of two skins of material with a spacing core of transverse cellular construction, wherein the panel is such as to have ratio of bending stiffness (B), in all orientations, to the cube power of panel mass per unit surface area (xcexc) of at least 10;
a mounting means which supports the panel or attaches to it a supporting body, in a free undamped manner;
and an electro-mechanical drive means coupled to the panel which serves to excite a multi-modal resonance in the radiator panel in response to an electrical input within a working frequency band for the loudspeaker.
U.S. Pat. No. 4,506,117 of MULTIPHONIE discloses an electroacoustic transducer comprising an inertial mass adapted to be attached rigidly by its base plate to a panel to be vibrated.
Embodiments of the present invention use members of nature, structure and configuration achievable generally and/or specifically by implementing teachings of our co-pending parent application Ser. No. 08/707,012. Such members thus have capability to sustain and propagate input vibrational energy by bending waves in operative area(s) extending transversely of thickness often but not necessarily to edges of the member(s); are configured with or without anisotropy of bending stiffness to have resonant mode vibration components distributed over said area(s) beneficially for acoustic coupling with ambient air; and have predetermined preferential locations or sites within said area for transducer means, particularly operationally active or moving part(s) thereof effective in relation to acoustic vibrational activity in said area(s) and signals, usually electrical, corresponding to acoustic content of such vibrational activity. Uses are envisaged in co-pending parent application Ser. No. 08/707,012 for such members as or in xe2x80x9cpassivexe2x80x9d acoustic devices without transducer means, such as for reverberation or for acoustic filtering or for acoustically xe2x80x9cvoicingxe2x80x9d a space or room; and as or in xe2x80x9cactivexe2x80x9d acoustic devices with transducer means, such as in a remarkably wide range of sources of sound or loudspeakers when supplied with input signals to be converted to said sound, or in such as microphones when exposed to sound to be converted into other signals.
This invention is particularly concerned with active acoustic devices in the form of loudspeakers.
Members as above are herein called distributed mode radiators and are intended to be characterised as in the above copending parent application and/or otherwise as specifically provided herein.
The invention is an inertial vibration transducer for exciting a member having capability to sustain and propagate input vibrational energy by bending waves in at least one operative area extending transversely of thickness to have resonant mode vibration components distributed over said at least one area and have predetermined preferential locations or sites within said area for transducer means and having a transducer mounted on said member at one of said locations or sites to vibrate the member to cause it to resonate forming an acoustic radiator which provides an acoustic output when resonating, comprising a motor coil assembly having a coil rigidly fixed to a tubular member, a magnet assembly disposed concentrically, with respect to the motor coil assembly, and a resilient suspension supporting the magnet assembly for axial movement relative to the motor coil assembly, and wherein the tubular member is adapted to be rigidly mounted directly to the member to be vibrated by adhesive means. The resilient suspension may comprise mutually opposed elastomeric members disposed on opposite sides of the magnet assembly. Caps may be provided for closing the axial ends of the tubular member, and the resilient suspension may be mounted on the caps. The caps may comprise the resilient suspension. Each cap may comprise an annular compliant roll surround. Magnetic shields may be provided over the caps. The coil may be mounted on the inner face of the tubular member. The motor assembly may be adapted for reception in a correspondingly shaped cavity in the radiator. The motor coil assembly may be adapted to be rigidly fixed to a face of the radiator. The magnet assembly may comprise opposed generally disc-like pole pieces, the periphery of one of which is disposed within and adjacent to the motor coil assembly, and the periphery of the other of which pole pieces is formed with a flange arranged to lie adjacent to and to surround the motor coil assembly. A resilient member may be sandwiched between one of the pole pieces and a face of the radiator. The magnet assembly may comprise an opposed pair of magnets sandwiching a pole piece. Complementary magnet assemblies and motor coil assemblies may be arranged on opposite faces of the radiator, and a fastener may be provided tying the magnet assemblies together for push-pull operation.
From another aspect the invention is a loudspeaker comprising an inertial transducer as described above.